Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $62.47   6.112%   $66.2882   $66.29   $66.30   $66.30  
  Purchase #2 $218.92   12.694%   $246.7097   $246.71   $246.70   $246.70  
  Purchase #3 $239.34   13.322%   $271.2249   $271.22   $271.20   $271.20  
  Purchase #4 $14.32   5.272%   $15.075   $15.08   $15.10   $15.10  
  Purchase #5 $128.35   4.323%   $133.8986   $133.90   $133.90   $133.90  
  Purchase #6 $184.72   3.638%   $191.4401   $191.44   $191.45   $191.40  
  Purchase #7 $223.90   9.301%   $244.7249   $244.72   $244.70   $244.70  
  7 purchase totals = $1,072.02       $1,169.3614   $1,169.36   $1,169.35   $1,169.30